Electrical heating apparatus and method



Aug. 7, 1928.

A. s. MACDONALD ET AL ELECTRICAL HEATING APPARATUS AND METHOD Filed July 17, 1925 s sheets-sheet l Aug. 7, 1928.

A. S. MACDONALD ET AL ELECTRICAL HEATING APPARATUS AND METHOD Filed July 17, 1925 5 Sheets-Sheet 2 INV NT NEX;

Aug. 7, 192s. `1,679,730

A. S. MACDONALD ET AL ELECTRICAL HEATING APPARATUS AND METHOD Filed July 17, 1923 3 Sheets-Sheet 3 Mfr/.4755 l lNvE/vroze A TTORNEY Patented 7, 1928.

UNITED STATES ANGUS s. MACDONALD, E GREAT NECK,

1,619,730 PATENT OFFICE.

NEW YORK, AND CHARLES C. WAITE, OF

ROSELLE PARK, NEW JERSEY, ASSIGNORS TO SNEAD & COMPANY, 0F JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ELECTRICAL HEATING APPARATUS AND METHOD.

Application filed July 17, 1923. Serial No. 652,047.

Our invention relates to electrical heating apparatus and methods, and is more especially concerned with the heating of articles hy passage .ot currentthrough them. This inode ot' heating is very advantageous in the case ot metal bars or rods,-including hollow rods or tubes,-f0r the purpose of annealing. tempering, or otherwise heat treating them.

Inheating an article in this manner, electrical Connection is generally made to it by means of terminals or clamps (pas they y are called), by which the ends of the article are engaged. Naturally. such clamps tend r to conduct heat away VJfrom the article. so

that the portions at and adjacent the clamps do not attain so high a temperature as the intermediate main body of the article. As the range. of temperatures within which the best effect on the article can be produced is often a rather narrow one/. too high a temperature heiiig as had as one too low the portions affected hy the cooling action of the clamps are often of such poor qualitv that they have to be cut oft' and scrapped..

For example` in annealing brass condenser tubing by passage of current, it is sometimes toundinecessary to discard as much as six` inches or more ott' each end oteach tube.

lVe aim to obviatc this drawback of such electrical heating by preventing or minimizing loss ot heat at the clamps. Practieallv. we have found, this can he accomplished to advantage by heating the clamps and bv reducing their thermal conduction,- preferably both. The heating of the 'clamps for this purpose can most conveniently be. efl'ected by passage of current. l-low various objects and ,advantages can he realized through our invention in a novel manner will appeal' trom our description hereinafter of the. best methods and apparatus for the purpose known to us.

lnl the drawings, Fig. l 1s a somewhat diagrammatic side elevation ot an apparatusltor electrically heating rods or tubes hy passage of current through them. convenientlv embodying our invention.-a middle portion being broken out and omitted. h

Fig. 2 is a Wiring diagram illustrating electrical connections for heating both tube and clamps in the machine of Fig. 1.

Fig. 3 is a fragmentary side view of the clamps at one end of the tube as shown in Fig. 1, on a larger scale.

Fig. 4 is a View of the clamps from the right of Fig. 3, the tube appearing in seiction.

Figs. 5 and 6 are views similar to Figs. 3 and 4, illustrating a different form of clamp.

Fig. 7 is a diagram illustrating a mode ofheating the,clamp somewhat diiferent from that of Fig. 2.

Fig. 8 is a diagram illustrating still another mode of heating the clamps.

Figs. 9 and 10 are diagrams illustrating provisions for varying and regulating the heating of the clamps.

Figs. 11 and 12 are edge and side views of a different form or type of clamp device.

Fig. 13 shows a longitudinal section through still another type of clamp device.

Fig. 14 is a side view of one of the parts shown in Fig. 13.

The apparatus'illustrated in Fig. 1 is substantially that described and claimed in the pending application of Macdonald, l/Vaite & Huggins, Serial No. (iS-39,231, tiled May 16, 1923, and assigned to the assignee of this application. For the purposes of this aliplication, it may be. suliciently described as comprising clamping heads 1() and 11 carried by carriages V12 and 13 mounted on timber ways 14. Either or both of the carriages 12 and 13 may be shifted along the ways 14 to take care of differences in length of pieces to be treated. In addition, the clamping head 11 is shiftable to.

take care ot variation in length of the piece P undergoing treatment with change of temperature, by virtue ot being mounted on rollers 15 rolling on ways 1G carried by the main body ot the carriage 13, that rests directly on the ways 14. ln order that such resistance to movement along the Ways 16. as the head 11 may otter shall not' tend to buckle the piece l. as it expands with heating, a weight 17 is connected with the head 11 by a cord 18 passing over a pulley sheave 19. If heavy enough, this Weight 17 will not only take up the expansion of the piece l", but will also exert tension on it, so as to straighten out any kinks in the piece While the latter is hot and soft. A treadle 2O connected to the head 11 by a cord 2,1 also passing over the sheave 19 affords a convenient means of returning the head 11 each time to the desired initial position for the next heat. As shown, each of the heads 10 and ll has a pair of opposed clamping jaws 22, 22, one conveniently adjustable by means of set screws 24, 25, and the other operable by a spring and opposing solenoid arrangement 26, 27. At the end of each heat, the current through the piece P is shut off and the movable clamping jaws 22 are opened.

As shoivn in Fig. 2, current to heat the piece P is supplied from. an A. C. power line 30 (at 22() volts, say), through a switch 31 and a transformer 32 with adjustable secondary. As shown, the secondary leads and 34 from the transformer 32 divide at each of the clamping leads 10 and 1l, so that the heating current for the piece traverses each pair of clamps 22, 22 in parallel. In the apparatus illustrated in Fig. 2, the current thus Supplied the piece P through the clamps 22, 22 is also relied on to heat the clamps. For this purpose, the clamps 22, 22 may preferably be made of metal of suitably high electrical resistance and refractory character, such as nichrome2 so that they can adord ample area of contact with the piece P, and thus minimize heating` effects at' the-portions Which engage it, and still be of sufficient total resistance to heat adequately. IVith this arrangement, it will be seen, the adjustment at the transformer 32 that varies and regulates the current in reference to the heating of the piece P can also be made to serve for varying and regulating it in reference to the heating of the clamps.

While the heat developed as a. result of the kContact resistance between t-he piece l and the clamps 22; 22 tends, of course, to counterbalance their conduction of` heat away from the piece, it is usually desirable not to lhave the contact resistance high enough to compensate entirely for thermal conduction. in

order to avoid risk of excessive local heating at the contacts, but rather to proportion the clamps to reduce their thermal conduction and increase their electrical resistance sufficiently to bring about a balance. As shown in Figs. l. 3 and 4, each ofthe clamps 22,- 22 is reduced in effective cross section and thus specially heated, for this purpose,

at a point behind the piece-engaging portion.v In t 1s particular instance, each clamp 22 is formed of a metal plate or strip with its end round-notched in conformity 'to the tubular piece shown, and with its longitudinal edges also reduced or notched for a considerable length to reduce its effective cross section and electrical conductivity. The shank or butt is of full Width, so as to afford ample conductivity and Contact surface for securing it to the head.

Figs. 5 and 6 illustrate another way of reducing the cross section without so greatly diminishing the strength and rigidity of the clamp in a transverse direction in its own plane. Here the clamp plates 22, 22 are each perforated with a multitude of holes 36 (arranged in rows and staggered) for a suitable length behind their piece-engaging extremities.`

In Fig. 7, main reliance for specially heating the clampslO, 40 shown is placed on current supplied lfor this purpose from a separate (A. C. or D. C.) source 4l. As shown the cooperating jaws 40, Ll0 are connected in thejaw-heating circuit in parallel, and are traversed by suclrcurrent in a general direction at right angles to the general flow of clamp-heating current. As here indicated, the reduction in effective cross section of the high-.resistance metal clamp pieces Ll0, Lll0 due to their piece-engaging notches may be availed -of to assure adequate heating. In this case, the extent transversely of a jaw 40 of the highly conductive lead 33 for the piece-heating current is insignificant, so that such lead Will not act as a shunt to reduce the heating effect of the transverse current flow.

In Fig. 8, the clampsO, 50 are specially heated hy current from a separate source 51, but not in parallel; and instead of traversing the'clamps themselves, the current flows through separate heating elements 52, 52,-here shown as in the form of external coils (of nichrome or other suitable metal) wound around the terminals. An adjustable resistance or rheostat 53 is included in the 100 heating circuit, as a convenient means for varying and regulating the heating current,

In Figs. 9 and 10, the clamps 60, G0 are specially heated in parallel by the heating current for the piece P itself, as in Figs. l to 6; and the heating devices for this purpose consist of reduced portions of the clamps themselves behindtheir piece-engaging portions (note the rows of holes 36 as in Figs. 5 and 6), rather than of separate 110 resistance coils 52 as in' Fig. 8. In these figures, however, there are separate provisions for regulating and controlling the heat- Iing of the clamps G0, 60 by variably shunting portions of the clamps. As shown in Fig. 9, the shunt circuits 6l, 6l for this purpose extend from the more conductive pieceengaging portions ot' the pair of clamps 60, (3() around their reduced heater portions to their portions just behind the 12 holes 3G, and include a common connection with a rheostat or variable resistance G2 therein. In Fig. 10, these shunts Gl, (3l are similarly arranged, but include a variable inductance 63 instead of the rheostat G2.

In this way, it Will be seen. the heating of the clamps 60, 60 can be adjusted to a nicety notwithstanding considerable variations in the total heating current for the piece P, since the shunts 61, 6l can be ad- 130 yciently low thermal Conduction.

justed to carry a heavy current around the clamp heaters if need be. In this case, of course. the clamps 60, G0 are preferably made of high resistance material.

In Figs. 11 and 12 isshoWn a clamp or contact jaw specially heated effectively without reduction in cross section such as illustrated in Figs. 3 to G, 9 and 10. The

heating device of this jaw 70 consists of an intermediate portion 71 of high resistance material (such as nichrome) interposed (and Welded or otherwise secured) between contact and butt ends 72, 73 of copper or other highly conductive material. The high conductivity of the copper ends 72, 78 allows them to be made of such limited cross section that a -portion 7l of like section will heat amply on current insufiicient to heat the ends themselves much. andl will also have sulli- This type of clamp is adapted toa variety of circuit arrangements, including those shown in Figs. 2, 6, 9 and 10.

Figs. 13 and 14 illustrate a clamp or. jaw device 80 also specially self-heating Without cross sectional reduction. Here the jaw member 81 proper may be of copper or other highly conductive material throughout, and may be made readily detachable from the heating device 82 to permit of e'asy replacement. As shown, the heating device 82 comprises a strip of high resistance material 83 (such as nichrome) interposed or .sandwiched between strips of electrical insulation 84, 85 and inner and outer protective facing plates 86, 87, ofI copper or the like. The heating strip 83 is in connection with the inner facing 86 adjacent the piece-engaging end of the jaw member 81, by direct contact ivith-its thickened end, and is in connection with the outer facing 87 at the other end, by contact of both with an interposed copper collar or block 88. The bolts 89 that secure the parts together may be insulated from the 4facing 87 and collar 88, as shown.

The main heating current lead 90 is connected to the'puter facing 87. so thatthe current traverses the length of the heating strip 83 on its ivay to the jaw piece 81, which it reaches close to its piece-engaging end.

The jaw piece 8l lies snug against the innerv facing 86, and* is heated by conduction through the latter and the thin layer of electrical insulation 84. Thus the current for heating the piece (not shown in Figs. 13 and 14) also heats the clamp device. A shunt connection' with current regulating means 91 (shown asa variable inductance) may be provided to the upper end of the jaw member 81, as a means of controlling 'the proportion and amount of current tiow through the strip 83, and so regulating the heating.

What we claim is:

1y A' method of preventing deleterious cooling, by terminal clamps, of a piece electrically heated by passage of current through it, without riskof excessive local heatineq effect-s at the contacts between clamps and piece; which method comprises specially heating, by passage of electric current, portions of the clamps behind those Which engage the' piece, while minimizing heating effects at the latter portions.

- 2. A method of preventing deleterious cooling, by terminal clamps, of a piece electrically heated by passage of current through it, Without risk of excessive local heating effects at the contacts between clamps and piece; which method comprises minimizing heating effects at the portions of the clamps that engage the piece, and specially heating portions of the clamps behindthose which engage the piece sutiiciently to compensate for the difference between the conduction of heat by the clamps and the heating effect of their contact resistance.

3. A method of preventing deleterious cooling, by terminal clamps, of a pieceelectrically heated by passage of current through it, Without risk of excessivelocal heating effects at the contacts betweenclamps and piece;-Which method comprises minimizing heating effects at the portions of the clamps that engage the piece, and specially heatingV portions of the clamps behind those which engage the piece, variably shunting such ispecially heated portions to regulate their ieat.

4. .Apparatus for heating by passage of current comprising terminal clamps for a piece' to be treated, withy means for passing current through the piece to heat it and means for specially heating portions of the clamps behind thosewhich engage the piece.

5. Apparatus for heating by passage of current comprising terminal clamps for a piece to be treated, with means for passing current through the piece to heat it, means for specially heating portions of theclamps behind those which engage the piece while minimizing heating effects at said engaging portions, and means for varying andl regulating the current for the specially heated portions of the clamps. y

6. ApparatusI for heating by passage of current comprising a terminal clamp with a resistance heater device behind its conductive piece-engaging portion, and a variable shunt for said heater device for regulating the heating of the clamp.

7. Apparatus for heating by passage of current comprising terminal clamps for pieces to be treated heated by passage therethrough of the current for heating the piece, and means'for variably shunting portions of the clamps behind those engaging the piece to regulate the heating of the clamps.

8. Apparatus for heating by passage of current comprising' a terminal clamp havingv a piece-engaging portion affording adequate area for transmission of heating current to the piece, and locally reduced in cross section behind such portion to cause heating thereof by the heating current, and a variable shunt from such piece-engaging portion around such reduced portion for regulating the heating-effect of the latter.

9. A terminal clamp for pieces to be heated by passage of current locally reduced in cross section behind its piece-engaging portion to cause heating of the clamp by the heatingr current for the piece.

l0. A terminal clamp for pieces to be heated by passage of current having a pieceengaging portion affording adequate area of contact for transn'iission of current to the piece, and locally' reduced in cross section behind its pieceengaging portion to bring'the thermal conduction and the electrical heating effect substantially to a balance.

1l. A terminal clamp for pieces to be heated 'by passage of current having a highly conductive piece-engaging portion, and a heater portion of high resistance behind such piece-engaging portion.

l2. A terminal clamp for pieces to be heated by passage of current through the pieces, comprising a heater device and ajaw member detachably secured thereto.

13. A terminal clamp for pieces to be heated by passage of current through 'the pieces, comprising a jaw member and a. heater'device therefor. y

let. A terminal clamp for pieces to be heated by passage of current comprising a jaw member, and a heater device therefor including a heat-ing strip connected to said member at one end and to a current lead at the other, with a-layer of electrical insulation between said heating strip and said jaw member.

15. A terminal clamp for pieces to be heated by passage of current comprising a jaw member, and a heater device against one side thereof comprising a heating strip 'sandwiched between insulative layers and conductive facing plates.

lu testimony whereof,l we signed our names.

ANGUS S. MACDONALD. CHARLES C. VAITE.

have hereunto 

